A study found that moms of autistic children were more likely to report using household pesticides, like those in pet shampoos.
(Tracy Morgan/Dorling Kindersley/Getty Images)
Scientists also must determine what pyrenthrins do to the brain, and when.
People know what pyrenthrins do to insects -- kill them -- and they know it affects rats, but that doesn't mean researchers know everything that pyrenthrins can do to human brains.
In rats, pyrenthrins weaken the blood-brain barrier, which helps to keep potential toxins in the bloodstream out of the brain. "Drawing a conclusion about what the effect will be on the human brain is a bit of a jump," Krug said.
Even the known fact that pyrenthrins kill neurons -- the brain cells responsible for sending signals in the brain -- only raises more questions about the link to autism
"The key there is that pyrenthrins might cause death of neurons, but in autism there's no evidence that the death of neurons is the trigger," said Eric Courchesne, professor of neuroscience at the University of California San Diego School of Medicine.
"In fact just the opposite, it might be an excess of neurons," said Courchesne. A few years ago, Courchesne and his colleagues found that children with autism showed brain overgrowth in the first two years of life, raising the question of how chemicals that kill off brain cells are also responsible for extra brain cells.
As it stands, Courchesne and other doctors aren't sure what it is about the brain growth that triggers autism. "You could have the brain growing too fast, so maybe neurons grow too rapidly, maybe they generate too many connections in some regions, maybe two few in other regions," Courchesne said.
The pyrenthrin study now also intrigues him. "From my perspective, the finding is very interesting and very important," said Courchesne, who explained that while autism is largely due to genetics, most scientists recognize some outside factors contribute too.
"It's clearly important to understand whether there might be environmental agents that interact with genetics to increase the chances of autism," he said. Now Courchesne hopes there will be more animal models with pyrenthrins and brain growth.
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